Photorelay and method of increasing the accurate useful life thereof



y 7, 1957 c. CHILOWSKY 2,791,652

PHOTORELAY AND METHOD OF INCREASING THE ACCURATE USEFUL LIFE THEREOF Filed Jan. 10. 1955 INVENTOR n w o-w ATTO R N EYS United States Patent PHOTORELAY AND METHOD OF INCREASING THE ACCURATE USEFUL LIFE THEREOF This invention relates to a method and apparatus for increasing the life of photorelays, particularly such photorelays as those disclosed in applicants U. S. Patents No. 2,024,966, No. 2,150,050, No. 2,150,051, No. 2,153,456 and No. 2,243,596, which utilize the catalytic action of actinic light upon the chemical reaction, at ambient temperatures, between chlorine and hydrogen.

Such apparatus comprises a glass bulb or ampoule partially filled with an aqueous solution of HCl containing some free chlorine which is submitted to electrolysis by means of suitably placed electrodes connected to a source of direct current. This electrolysis, of constant voltaic intensity, releases the gases hydrogen and chlorine, which accumulate as a mixture in the space above the liquid where their re-combination (and redissolving) is a function of the intensity of the light to which the mixture is exposed. The fluid system is in equilibrium when the electrolytic release is at the same rate as the catalytic re-combination; when the light is reduced the rate of recombination drops and the volume of free gases increases; when the light increases, the free gases combine faster and the volume of the gases is reduced. These volumetric variations are applied to a diaphragm or to a mercury column to effect the openings and closing of electric circuits, in function of the ambient light; for example, to turn on lights at the approach of darkness and to extinguish them upon the return of daylight.

Experience over a period of years has shown that the photosensitivity of the unit slowly but progressively changes, presumably due to some complex physicochemical phenomena resulting in irreversible reactions (particularly near the electrodes) which irreversibly disturb the equilibrium of the gases, hydrogen, chlorine and oxygen. Although such changes are slow, they have the obvious result of altering the operating characteristics of the photorelays, so that initial calculations of speed, sensitivity, etc., do not remain valid.

It is an object of the present invention to remedy this ditliculty so that the accurate life of the photorelay is greatly extended.

A further object is to increase the accuracy and reliability of operation of the photorelay.

Another object is to broaden the field of utility for such photorelays, in respect of the conditions in which they are required to operate.

A still further object is to provide certain improvements in the form, construction and materials of the several parts and in the steps of the method whereby the abovenamed and other objects may effectively be attained.

With these objects in view, a capacity of relatively great volume, completely filled with the electrolite (aqueous solution of HCl, preferably containing some free chlorine), is placed between the electrolytic bulb or ampoule and the flexible diaphragm or the like. The liquid in said capacity may have a volume, for example, ten to twenty times greater than the volume of liquid normally present in the ampoule. This supplementary liquid constitutes a reserve supply of relatively fresh solution which is utilized to maintain for a long time a substan tially constant composition of the liquid in the ampoule and, consequently, of the gaseous atmosphere in the ampoule above the liquid; the composition of the gases remaining always in equilibrium with the composition of the liquid.

For this purpose the ampoule is connected with the reserve capacity by a very narrow passage (e. g., a capillary tube) of such length that there can be no appreciable diffusion of gas from the ampoule toward the reserve capacity, at least during the period of a normal cycle of operation of the device. On the other hand, the total volume of the passage is smaller than the volume of displacement required for operating the electric contact, so that during the darkening phase of the cycle of operation a small quantity of the liquid from the ampoule is projected into the reserve capacity, and during the lightening phase of the cycle a similar quantity of the liquid from the reserve capacity is drawn into the ampoule. Due to the dilfusing characteristics of liquids it is obvious that the liquid drawn into the ampoule will include an appreciable quantity of relatively fresh liquid. The liquid in the ampoule is thus maintained at a satisfactory degree of freshness for a period of time which exceeds the comparable life of a device without reserve capacity in a ratio approximately equivalent to the ratio between the volume of the reserve capacity and the volume of the liquid in the ampoule.

Other improvements include the provision of pure iridium electrodes for the electrolysis and also the use of special diaphragms capable of operating with greater amplitude, so that electric currents of greater power can be directly controlled.

Practical embodiments of the invention are represented in the accompanying drawings, in which Fig. 1 represents a vertical axial section through one form of photorelay;

Fig. 2 represents a detail diametrical section, on a larger scale through the diaphragm of Fig. 1;

Fig. 3 represents a similar section of a modified form of diaphragm;

Fig. 4 represents a similar section of the diaphragm portion of a photorelay, in which a diaphragm like that of Figs. 1 and 2 is mounted between guard plates of a modified form; and

Fig. 5 represents a vertical section corresponding to to the upper portion of Fig. 1 with the addition of heating means;

Referring to the drawings, and particularly to Fig. 1, the photorelay is shown a comprising a glass bulb or ampoule 1, from the bottom of which depends a tubular stem 2 provided with a capillary channel or passage 3. The ampoule 1 is fluid-tightly secured in the top of a rigid container 4 constituting the reserve capacity and the stem 2 projects downward therein for a substantial distance. The lower edge of the container 4 is provided with an outwardly extending flange 5 and the bottom of the container is closed by a membrane or diaphragm 6, preferably mounted between an upwardly convex glass guard plate 7 and a downwardly convex glass or metal guard plate 8. The peripheral edges of the daiphragm 6 and plates 7 and 8 are supported on the inwardly projecting shoulder 9 of a frame 10, said edges being held firmly together and sealed to each other and to the flange 5, as by means of cement 11. The container 4 and passage 3 are completely filled, and the ampoule 1 is partly filled, with the electrolyte, constituted by an aqueous solution of HCl of moderate strength with some dissolved free chlorine.

The plates 7 and 8 limit the upward and downward deflection of the diaphragm, the plate 7 being perforated to permit free access of the liquid to the upper surface of: the diaphragm, and the plate 8 having a central opening for the passage of a rod 12 fixed to the middle of the diaphragm and projecting downwardly therefrom.

In the lower part of the ampoule 1 are mounted electrode 13,, Passing, through the. glassy walls, of the am- Pa la and. prejiecting. suitable distances into the enclosed space. The, electrodes, can be of platinum-iridium alloys, but it. is preferable. to use pure iridium which reduces to a minimum the accumulation of harmful impurities in the course of electrolysis, with the result that the purity of the. iridium alloysis a factor to be considered (inversely) in determining the volume of the reserve capacityfor a given effective life of the device. The electrodes 131 are part of a simple circuit indicated at 14, through which passes a; small current from a source 15, the. circuit. includingalso-a. fixed contact 16 and a complementary contact mounted on the movable spring arm 17 The arm 17: is so located that it is depressed by the downward movement ofthe rod 12, the first effect being tooperate the button 18 of a micro-switch 19, controlling an exterior lighting circuit,- for instance, connected to main'terminals 20, and the second effectbeing to break the electrolytic circuit at 16.

The membrane or diaphragm 6 of Fig, 1 is shown on a larger scale in Fig. 2 as comprising a sheet of platinumiridium having a thickness of a few hundredth of mm., formed in concentric annular undulations, and preferably protected on its upper side by a thin, strongly adherent, plating of glass or quartz 21.

Fig; 3 show an alternative form of diaphragm 22 comprising a thin flat disc of metal protected on its upper face by a thin plating of glass or enamel 23..

The guard plates 7 and 8 may be provided, a before, in order to limit the elastic deflections of the diaphragm, and a rod 24' is mounted at the middle of the diaphragm in order to operate a switch, as previously. explained. It is also possible to omit the metal and to form the diaphragm entirely of glass asshown, for instance, at 100 in Figs; 4a, 4b and 15 of Patent No. 2,150,050.

In Fig. 4 is shown another alternative form in which an undulated diaphragm 25- (similar to the diaphragm 6 of Figs. l andiZ)v is mounted between upper and lower guard plates 26, 27, the facing surfaces of said plates being formed in concentric annular undulations designed tofit exactly the upper or lower surfaces of the diaphragm 25 in its predetermined upper and lower limit positions of deflection.

Such'photorelays will operate satisfactory at ambient temperaturesydown to- C. or even C. and socan be used within buildings practically anywhere and outdoors in any'locality where temperaturesdo not go below -5 C; For outdoor installations in colder regions a simple automatic thermostatic heating system may be added,as-indicated'inFig. 5;

The heating circuit of Fig. 5' includes, in series, a lead? inwire 28, an insulated heating Wire 29 wound helically around the capacity 4, aheatingcoilfit) surrounding the lowerpart of the ampoule 1', a vertical post 31 mounted in an annular plate 32 0f. suitable insulating material, a; bimetallic arm 33 of generally arcuate form secured at one end to the. top of the post 31 andextending through- 180 more or less to the vicinity of the contact 34, which is alsomounted on the plate 32 and isconnected to a second lead inwire 35. It will normally be desirablettoenclose the photorelay and its heating system in a casing 36- of heat-insulating material of any desired thicknessbut provided with a large orifice-37 (or translucentarea) for admission of light to theampoule.

The-lead-in wires 28, 35' are connected to a suitable source of'alternatingheating current, not shown, and the gap between the free end'of the arm 33and'the contact 34-is set at a value such that it will. close when the. am;

bient-temperature reaches, for instance, 0C. or slightly 4 lower. The current can then fiow through the winding 29 to heat the reserve capacity and, more importantly, through the coil 30 to heat the ampoule and its contents at least sufiiciently to prevent its temperature from falling below -5 C. When heat from the coil 30 has raised the temperature of the arm 33 to a point where the gap is opened, the current will be shut off. The lag between closing or opening of the gap and heating or cooling of the parts is such that no objectionable hunting i likely to occur.

The winding 29 may be omitted entirely if the conditions of operation. are such that there is no danger of freezing of the reserve capacity. The ratio of heating of the ampoule and of the reserve capacity can be predetermined, as a function of the ratio of resistance of coil 39 to the resistance of winding 29, when the latter is present.

Assuming that the photorelay of Fig. l (with or withoutthe heating means of Fig. 5) is assembled in a. utilization system, with the. main terminals 2% connected to. a lighting circuit, for instance, which is to be closed upon the advent of darkness; so long as sufiicient light falls on. the ampoule 1 to cause chemical combination of-the hydrogen and chlorine gases at a faster volumetric rate than said elements are dissociated by the electric current between electrodes 13, 13, the total gas and liquid volume in the ampoule l and capacity 4 will appreach a minimum, the diaphragm 6 will be raised and the arm 17 will be in such position that the electrolytic circuit through the contact 16 is closed.

A reduction in the illumination on the ampoule 1 slows down the rate of combination of the gases. When that rate falls below the rate of electrolytic dissociation the volume of gas in the ampoule increases, forcing liquid through the passage 3 into the capacity 4 and, necessarily, pushing down the diaphragm 6. The rod 12 thereupon moves the arm 17- so as to actuate the button 18 of the micro-switch (closing the utilization circuit throughterminals 20) and then opens the electrolytic circuit between 16 and 17in order to stop the generation of additional pressure, which might be destructive. Thus, in darkness, the photorelay is at rest, but remains chemically ready to resume operation as soon as enough light again falls on the ampoule.

With each expulsion of liquid from the ampoule into the reserve capacity, followed by drawing liquid again from the capacity to the ampoule, there is a freshening of. the'supply in the ampoule as well as a dilution and dissipation of the used liquid and of any infinitesimal quantit-ies of impurities which may be suspended therein. The effect on the accurate life of the photorelay has been mentioned above. While the provision of the reserve capacity has been described in connection with only one specific type of photorelay, it will be apparent that the same modification can be made, with the same advantages, in other photorelays shown in the patents cited above, including those using a mercury contact.

it is desirable that the movable diaphragm in such apparatus be formed (whether flat. or undulated) of very thin metal, in the interest of strength and durability as compared to the glass diaphragms previously used. The metal should be heavier than a foil but still thin enough so that its bending movements will not crack the glass plating. Platinum alone or platinum-iridium may be used, because of their resistance to the chemical action of HCl, but. they. should nevertheless be glass plated with a coating of glass thinner than the metal in order to have a really useful life. Since glass plating is desirable in any event, it is preferable to form the metallic base of the. diaphragm from Kovar, an alloy containing approximately 20% Ni, 17% Co, 0.2% Mn and the balance Fe, which alloy has almost the same coefficient of expansion as certain glasses and so is particularly suited.

to'use in metal-glass assemblies (as in the case of the peripheral sealing of the parts 5, 6, 7, 3 in Fig. l).

A special method of applying glass to metal consists in spraying a layer of finely atomized glass on the metal surface to be protected, followed by baking, as in enamel ing processes. Quartz or silica may also be used instead of glass, and the application may be effected as described in applicants Patent No. 2,445,310 of July 20, 1948. For additional security a diaphragm of Kovar could be covered first with a thin protective deposit of platinum or platinum-iridium over which is applied the glass layer.

in further explanation of the glass spraying method, it may be noted that this involves projecting a fine glass powder, by means of a high temperature gas combustion jet, into water or on the Water surface, where the very small incandescent glass particles burst or explode into submicroscopic particles. The suspension of such particles is concentrated and then applied to the surface to be coated, followed by baking.

The permissible thickness of the glass layer, in any case, depends on the amplitude of movement of the diaphragm. The use of non-undulated diaphragms of glass alone or of metal and glass (Fig. 3) has the effect of reducing the amplitude of motion of the rod 24 (as compared to rod 12 in Fig. 1) and thus, in general, reducing also the power which can be controlled.

If it is assumed that the volume displacement of the diaphragm (6, 23 or 25) necessary to actuate the contact arm 17 effectively in either direction is equal, for instance, to mm. and if the volume of the electrolytic liquid in the ampoule is 500 mm. /2 cc.), it will be apparent that each complete cycle of operation involves the expelling of about 1% of the liquid in the ampoule and the replacement thereof by an equal quantity of liquid from the reserve capacity, which may have a volume of cc. to 20 cc. Without attempting to distinguish sharply between used liquid and fresh liquid, there will be a continuous slow interchange of liquid between the ampoule and the reserve capacity such that the active accurate life of the device will be greatly extended. For example, a device which operates with practical accuracy for about a year Without reserve capacity can, according to the invention, operate accurately for at least 5 or 10 years.

Because of the very great chemical activity of the nascent chlorine produced in the operation of such a photorelay, the materials which can be used for parts exposed to the chemicals are distinctly limited, as must be evident. Among the thousands of plastics now known, the one which appears to offer the most promise as a diaphragm material is the tetrafluoroethylene polymer known as Teflon, and use of this material as an alternative for the glass-covered metal discussed above is to be recognized as a possibility.

It will be understood that various changes may be made in the form, construction, arrangement and materials of the apparatus and in the steps of the method, and hence I do not intend to be limited to the details shown and described.

What I claim is:

l. A photorelay of the character described comprising, a translucent ampoule containing a quantity of hydrochloric acid solution with some dissolved free chlorine and a quantity of mixed hydrogen and chlorine gases, a reserve capacity having a volume substantially greater than the volume of the solution in the ampoule and being filled with hydrochloric acid solution, with some dissolved free chlorine, a substantially capillary passage connecting the ampoule and the capacity, means for causing electrolysis of the solution in the ampoule, whereby hydrogen and chlorine gases are released tending to increase the total volume of the contained fluids, a movable element operatively associated with the reserve capacity and kinetically responsive to variations in said total volume, and a utilization system control operatively associated with said movable element.

2. A photorelay according to claim 1 in which the volume of the capillary passage is less than the difierence between normal operating maximum and minimum total volumes of the contained fluids.

3. A photorelay according to claim 1 in which the means for causing electrolysis includes an electrolytic circuit having electrodes in contact with the solution contained in the ampoule, said electrodes being of substantially pure iridium.

4. A photorelay according to claim 1 in which the means for causing electrolysis includes an electrolytic circuit having electrodes in contact with the solution contained in the ampoule, said electrodes being of iridium the purity of which is predetermined as a factor in the intended useful life of the photorelay.

5. A photorelay according to claim 1 in which the ratio of volume of the solution in the reserve capacity to the volume of the solution in the ampoule is predetermined as a factor in the intended useful life of the photorelay.

6. A photorelay according to claim 4 in which the ratio of the volume of the solution in the reserve capacity to the volume of the solution in the ampoule is also predetermined in relation to the purity of the iridium as coordinate factors in the intended useful life of the photorelay.

7. A photorelay according to claim 1 in which the volume of the reserve capacity is at least several times greater than the volume of liquid solution in the ampoule.

8. A photorelay according to claim 1 in which the movable element comprises a metallic diaphragm protected on its surface in contact with the solution by a thin continuous deposit of material selected from the group consisting of glass, enamel or quartz.

References Cited in the file of this patent UNITED STATES PATENTS 

